ORIGINAL ARTICLESPlatelet microparticle suppressing antibody against GP Ibα acts independently of the filamin cleavage and increases protein tyrosine phosphorylationForestier, Marcb,*; Reséndiz, Julio Cc,*; Pontiggia, Lucab; Lassila, Riittac; Beer, Juerg Ha,bAuthor Information aDepartment of Medicine, University Hospital of Bern, Switzerland bDepartment of Medicine, Laboratory for Thrombosis Research, Kantonsspital Baden, Switzerland cWihuri Research Institute and Unit for Coagulation Disorders, Department of Hematology, Helsinki Central University Hospital, Helsinki, Finland * These authors contributed equally to this work. Received 21 February, 2008 Revised 11 July, 2008 Accepted 12 August, 2008 Correspondence to J.H. Beer, MD, Department of Medicine, Kantonsspital Baden, 5404 Baden, Switzerland Tel: +41 56 486 25 02; fax: +41 56 486 25 09; e-mail: firstname.lastname@example.org Blood Coagulation & Fibrinolysis: December 2008 - Volume 19 - Issue 8 - p 801-806 doi: 10.1097/MBC.0b013e3283177b43 Buy Metrics Abstract Our aim was to investigate the role of filamin cleavage and protein tyrosine phosphorylation in shear-stress-induced platelet microparticle formation and of its suppression by the monoclonal antibody (mAb) Ib-23 directed against GPIbα. PPACK-anticoagulated or EDTA-anticoagulated platelet-rich plasma or washed platelets were exposed to high shear stress (5000 s−1 for 5 min) in the presence of antagonists of GP Ibα (mAb Ib-23), of GP IIb/IIIa (abciximab) and their combination. We assessed the generation of microparticle by flow cytometry, the filamin cleavage and the protein tyrosine phosphorylation by western blotting. Microparticle formation decreased by more than 50% with mAb Ib-23 alone (P < 0.01, n = 23) but filamin cleavage was not inhibited. In contrast, abciximab did not change microparticle numbers nor filamin cleavage under the same conditions. However, when combined, the inhibitors against GP Ibα and GP IIb/IIIa decreased microparticle by 70% and the filamin cleavage by 20% (P < 0.05). Focal adhesion kinase and p72Syk phosphorylation was enhanced by mAb Ib-23, whereas treatment with abciximab reduced it. mAb Ib-23 inhibits platelet microparticle induced by high shear stress. The mechanism seems not to depend on filamin cleavage: abciximab allowed for full microparticle formation at similar levels of cleaved filamin, whereas the combined inhibitors reduced it. The effect of mAb Ib-23 on protein tyrosine phosphorylation supports previous data, which correlates microparticle formation with the extent of protein tyrosine dephosphorylation and mirrors the dephosphorylation by protein tyrosine phosphatase (PTP-1B) in platelets of calpain−/− knockout mice. © 2008 Lippincott Williams & Wilkins, Inc.